Thermostatic switch

ABSTRACT

A trip-free manual reset thermostatic switch with a thermostatic element for actuating a switch assembly by means of an actuator. The thermostatic element is mounted for flexing movement on a base and moves from a first to a second position relative to the base in response to predetermined temperature conditions, and then remains in the second position independent of further changes in temperature. The base and thermostatic element are provided with a cover movable toward and away from the base and held captive thereto. A switch assembly is mounted within the cover. This assembly includes a first contact secured to the cover and a contact arm one end of which is also secured inside the cover and having a free end carrying a second contact normally engaged with the first contact but movable out of engagement therewith. When the thermostatic element moves into its second position, the actuator concurrently moves the contact arm to separate the contacts. The cover, when moved from a normal to a reset position relative to said base, moves the actuator to bias the thermostatic element away from its second and toward its first positon, but the contacts will remain separated and the thermostatic element will not move into its first position while said element is subject to the predetermined temperature conditions. However, the contacts will reclose and the thermostatic element will be moved into its first position in the absence of the predetermined temperature conditions.

United States Patent [191 Blanton Aug. 27, 1974 THERMOSTATIC SWITCH [75]lnventor: Bobby D. Blanton, Garland, Tex.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 23, I973 [21] Appl. No.: 381,959

[52] US. Cl 337/354, 337/56, 337/72, 337/348, 337/358, 337/368 [51] Int.Cl. HOlh 37/52 [58] Field of Search 337/56, 92, 73, 74, 91, 337/348,350, 367, 368

[56] References Cited UNITED STATES PATENTS 2,374,778 5/l945 Platz337/72 3,272,941 9/l966 Sullivan 337/56 X 3,308,255 3/l967 Faggiano337/367 3,675,178 7/l972 Place 337/348 3,750,076 7/l973 Hines 337/561 X[57] ABSTRACT A trip-free manual reset thermostatic switch with athermostatic element for actuating a switch assembly by means of anactuator. The thennostatic element is mounted for flexing movement on abase and moves from a first to a second position relative to the base inresponse to predetermined temperature conditions, and then remains inthe second position independent of further changes in temperature. Thebase and thermostatic element are provided with a cover movable towardand away from the base and held captive thereto. A switch assembly ismounted within the cover. This assembly includes a first contact securedto the cover and a contact arm one end of which is also secured insidethe cover and having a free end carrying a second contact normallyengaged with the first contact but movable out of engagement therewith.When the thermostatic element moves into its second position, theactuator concurrently moves the contact arm to separate the contacts.The cover, when moved from a normal to a reset position relative to saidbase, moves the actuator to bias the thermostatic element away from itssecond and toward its first positon, but the contacts will remainseparated and the thermostatic element will not move into its firstposition while said element is subject to the predetermined temperatureconditions. However, the contacts will reclose and the thermostaticelement will be moved into its first position in the absence of thepredetermined temperature conditions.

14 Claims, 8 Drawing Figures BACKGROUND OF THE INVENTION This inventionrelates to thermostatic switches and more particularly to trip-freemanual reset thermostatic switches.

Thermostatic switches are widely used to make or break electricalcircuits in response to the occurrence of preselected thermalconditions. One type of thermostatic switch will automatically resetitself to its original switching mode in response to a change in thermalconditions. In many instances a thermostatic switch is required thatwill trip the switch at a predetermined temperature but will not resetautomatically in normal usage. Such thermostatic switches, aretherefore, designed to be reset manually.

It is desirable that such manual reset type thermostatic switches betrip-free in operation, i.e., will not permit closing of the circuitwhenever the thermal conditions that cause tripping exist. While severaltypes of trip-free manual reset thermostatic switches are known,relatively complex structure has been required to jam the contacts orlock the switch contact arm or transfer pin, and a separate movable pinor push buttom has been necessary to effect resetting. Such additionalstructural components tend to adversely effect the reliability andtrouble-free operation of such units and substantially increase themanufacturing costs.

SUMMARY OF THE INVENTION Among the several objects of this invention maybe noted the provision of thermostatic switches that are manuallyresettable and trip-free; the provision of such thermostatic switches inwhich reset flexing of the switch contact arm and the need of separatereset buttons or pins are eliminated; the provision of such thermostaticswitches in which production costs are reduced and manufacturing issimplified; and the provision of manual reset trip-free thermostaticswitches which are easily and conveniently calibrated and are simple inconstruction and reliable in operation. Other objects and features willbe in part apparent and in part pointed out hereinafter.

Briefly, a trip-free manual reset thermostatic switch of this inventioncomprises a base, a thermostatic element, a cover for these components,a switch assembly and an actuator for the assembly operated by thethermostatic element. This thermostatic element is mounted for flexingmovement on the base and will move from a first to a second positionrelative to the base in response to predetermined temperatureconditions, and it will remain in this second position independent offurther changes in temperature. The cover provided for the base andthermostatic element is movable toward and away from the base and isheld captive thereto. The switch assembly is mounted within said cover.It includes a first contact secured to the cover and a contact arm oneend of which is also secured inside the cover and which has a free endcarrying a second contact normally engaged with said first contact butmovable out of engagement therewith. When the thermostatic element movesinto its second position, the actuator concurrently moves the contactarm to separate said contacts. The cover, when moved from a normal to areset position relative to said base, moves the actuator to bias theelement away from its second and toward its first position. However, thecontacts will remain separated and the thermostatic element will notmove into its first position while the element remains subject to thepredetermined temperature conditions. But in the absence of saidpredetermined temperature conditions, resetting movement of the coverwill reclose the contacts and the thermostatic element will be movedback into its first position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of a manualreset trip-free thermostatic switch of this invention illustrating thisswitch in a normal or untripped mode or condition with its contactsclosed;

FIG. 2 is a cross-section of the switch of FIG. 1 after tripping byoperation of the thermostatic element has opened the contacts thereof;

FIG. 3 is a cross-section of the switch of FIGS. 1 and 2, butillustrating the trip-free feature wherein the contacts cannot bereclosed while the thermostatic element remains subjected to the thermalconditions that actuated the switch assembly to a tripped mode;

FIG. 4 is a cross-section of the thermostatic switch of FIGS. 1-3, takenon line 4-4 of FIG. 1;

FIG. 5 is a cross-section of another embodiment of a thermostatic switchof this invention with the contacts in a tripped or open condition; and,

FIGS. 6-8 are cross-sections of still another embodiment of thisinvention showing the switch contacts in a normal or closed mode (FIG.6), a tripped or open condition (FIG. 7), and illustrating the trip-freeaspects thereof.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings andmore particularly to FIGS. 1-4, a manual reset trip-free thermostaticswitch of this invention is indicated generally at referencecharacter 1. Switch 1 includes a cup-shaped base 3, within which ismounted'for flexing movement a thermostatic element 5, an invertedcup-shaped cap or cover 7, a switch assembly 9 secured to the inner topportion of the cover, and an actuator 11. Preferably the base 3 isformed of metal and has an opening 13 permitting unobstructed heatexchange between the ambient atmosphere and the exposed undersurface ofthermostatic element 5 which is edge-supported on the periphery of adepressed central portion 15 of base 3. The thermostatic element 5 is asnap-acting composite thermostatic bimetallic disk such as disclosed inUS. Pat. No. 1,448,240. Because of the nondevelopable or dished shape ofdisk element 5, it will snap from one curvature position (FIG. 1) to anopposite curvature position (FIG. 2) upon the temperature increasing,for example, to a preselected level. As is known to those skilled in theart, these snap-acting bimetallic thermostatic elements may be sofabricated that under normal usage conditions the element can be cooledto ambient and lower temperatures after reversing curvature withoutresetting or returning to its original curvature. Thus it is a manualreset thermostat and will not automatically return or reset but must bephysically urged to snap to its normal curvature.

The operation or flexing of disk 5 from its first position (FIG. 1) toits other or second position (FIG. 2)

in response to predetermined temperature conditions elevates or movesupwardly actuator or transfer pin 11. This pin is axially slideable witha central bore 17 of a generally cylindrical pin guide 19 having arecessed undersurface 21 to accommodate the flexing movement of disk 5.Transfer pin 11 is fluted to minimize friction during axial movement ofthe pin within bore 17.

The upper end of pin 11 is spaced slightly away (FIG. 1) from a concaveintermediate portion 23 of a switch or contact arm 25 carrying onecontact 27 of switch assembly 9 on its free end. The other end ofcontact arm 25 is secured by cold welding or the like to the inner endof a terminal assembly 31 which extends through the cover 7 to provide aterminal lug 33 and is secured thereto thus firmly mounting contact arm25 on cover 7. Switch arm 25, as shown in plan in FIG. 4, is fan shapedwith a generally W-shaped relief slot 34. Another terminal assembly 35similar to assembly 31 is also secured to cover 7 and has an innerangled end portion 37 extending through its cover to which is welded, orotherwise secured, another or fixed contact 39 positioned for makingengagement by contact 27. Thus contact 39 is also firmly secured tocover 7 and is mechanically and electrically connected to a terminal lug41 of assembly 35. Switch arm 25 is so formed and mounted that itscontact is normally firmly biased 'upper surface of the intermediateportion 23 of switch arm 25.

Cover 7 and switch assembly 9 are a unitary assembly movable toward andaway from the base. The lower end of the cover 7 is outwardly flanged asindicated at 45 and is reciprocally movable axially toward and away fromthe base within an annular gage ring or sleeve 47. Ring 47 is securedwithin cup-shaped base 3 by the formation of an inwardly directed flange49. Annular sleeve 47 has a lip or overhanging flange 51 projectinginwardly from its upper margin and overlying cover flange 45 thusestablishing a stop or upper limit of travel for cover 7 which is biasedupwardly into a normal position (FIG. 1) by a spring or wave washer 53which is pocketed in an annular compartment 55 formed between theflanged lower surface of cover 7 and the upper surface of the outermargin of pin guide 19.

Cover 7, formed of insulating material, such as any molded thermosettingsynthetic material conventionally used for fabricating electrical switchhousings, has an upwardly projecting central lobe or button 57 which ispressed downwardly toward base 3 and against the bias of spring 53 toeffect resetting. Conventional electrical connectors may be connected toterminal lugs 33 and 41 to interconnect switch 1 into a circuit toeffect circuit-making or breaking functions in response to preselectedthermal conditions.

When, for example, the temperature of thermostatic element 5 rises abovesome predetermined level, it will snap from its normal position (FIG.1), in which the contacts 27 and 39 are closed, and move transfer pin 11upwardly to separate contacts 27 and 39 (FIG. 2). The transfer pin has alength slightly less than the distance between the undersurface ofconcave portion 23 of switch arm 25 and the upper surface of disk 5 whenin its cool or normal position (FIG. I). This provides a small degree oflost motion to permit the disk to creep slightly as its temperatureapproximates the preselected actuation temperature thus allowing someupward movement of the transfer pin without having it contact theundersurface of arm 25. As soon as the thermostatic element snaps to anopposite curvature, as shown in FIG. 2, the contacts of switch assembly9 are instantaneously opened.

If cover 7 is moved toward its reset position and toward base 3 bydownward manual pressure against lobe 57, post 43 will contact the uppersurface of portion 23 of switch arm 25 and apply force through pin 11 tothe central portion of disk 5, while depressing spring 53. If, however,the temperature of thermostatic element 5 is still above a preselectedresetting temperature, it cannot be caused to snap into its normal(FIG. 1) curvature before cover 7 bottoms relative to base 3. As long astransfer pin 11 continues to be urged upwardly by the still hot disk 5,contacts 27 and 39 remain open, as shown in FIG. 3. Thus, whilethermostatic element 5 is subject to the temperature conditions thatcaused it to move to its FIG. 2 curvature, the switch assembly 9 remainsin its open mode and is trip-free. Also, contacts 27 and 39 will beseparated, even if cover 7 is held in its reset position, upon thetemperature of disk 5 rising above its predetermined level and reversingcurvature.

The embodiment of FIG. 5 functions in the same manner as does thetrip-free manual reset thermostatic switch of FIGS. l-4, but differsstructually in two respects. Instead of a fixed reset post 43, as inFIGS. l-4, the FIG. 5 switch is provided with an optional movable oradjustable post 43a which is threaded and has a slotted top or outer end59 for adjustment in a threaded bore 61 of modified lobe 57a of cover7a. Post 43a constitutes a calibration screw which may be used'tocalibrate the temperature at which the thermostatic switch and itsthermostatic element may be reset. This is particularly useful inminiaturized switches built inaccordance with the invention. Byadjusting the distance, post 430 projects from the inner surface ofcover 7a, the thermostatic element will reset at different temperaturesthereof. Thus while the typical manual reset thermostatic element willnot under ambient temperature conditions of normal usage resetautomatically, it can be caused to reverse curvature or reset from itsFIG. 5 position at varying temperatures.

The other structural difference involves the omission of gage ring 47which is accomplished without losing the function thereof, viz., theestablishing of the amount and limits of travel of cover 7 relative tobase 3. In FIG. 5 the side walls of cup-shaped base 3a are provided withslots, one of which is illustrated at 63. During assembly, a spacerfinger or shim 65 is inserted to prevent compression of wave washer 53and establish the upper limit of travel or maximum displacement positionof cover 7 relative to the base. The upper edge of cup 3a is thencrimped to form inwardly directed flange 49a which directly overliesouttumed flange 45 of cover 7.

Referring now to a further embodiment, the trip-free manual resetthermostatic switch of FIGS. 6-8 functions in accordance with theprinciples of the present invention as described in regard to previousembodiments, but differs in that manual resetting is accomplished bymoving or pulling the cover away from the base. In this switchembodiment, a base 3b has a pair of integrally formed mounting ears andthermostatic element 5a provided with a central aperture 69 throughwhich projects a modified actuator or transfer pin or shaft 11a,preferably fabricated of an insulating material such as a syntheticresin material. The lower-end of 5 shaft 11a is flattened as indicatedat 71 and is spaced slightly below disk 5a in its normal position (FIG.6) to permit a small degree of lost motion so as to accommodate somedisk creep before it snaps at predetermined temperature conditions toits reverse curvature (FIG. 7). An enlarged upper end portion 73 ofshaft 11a which extends upwardly beyond the upper surface of a switcharm 25a (modified to have an aperture 75) has a head 77 spaced away(FIG. 6) from a central counterbore 79 of a modified button 57b whichhas a central bore 81 within which upper shaft extension 73 axiallyslides.

This thermostatic switch embodiment has a modified switch assembly 9asecured to and concertedly movable with cover 7a. In this instance afixed contact 39a is secured to the undersurface of a modified terminalassembly 35a with a laterally projecting terminal lug 41a, and a matingcontact 27a is mounted on the upper surface of a switch arm 25a, theother end of which is fixed to the inner end of a modified terminalassembly 31a. Switch arm 25a biases contact 27a to a normally closed orengaged position in firm contact with contact 390 in the normaloperating position (FIG. 6).

The lower edge of inverted cup-shaped cover 7a has an out-turned flange45a and spring washer. 53 is pocketed within an annular compartment 55aformed be tween the lower surface of lip 51 of sleeve 47 and the uppersurface of flange 45a thus urging or biasing the cover 7a toward base3b.

When thermostatic element 5a is subject to predetermined temperatureconditions, it will snap from its FIG. 6 curvature to that of FIG. 7 andmove pin or shaft 11a downwardly thereby tripping switch assembly 9a toopen contacts 270 and 39a. If cover 7a is moved away from base 3b andtoward its reset position as shown in FIG. 8, switch arm 25a and itsmovable contact 27a will remain spaced apart from contact 39a when thedisk 5a is subjected to the predetermined temperature conditions. In theabsence of such thermal conditions, however, thermostatic element 5awill manually reset and permit the switch assembly to return to thenormal contacts-closed condition illustrated in FIG. 6.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. A trip-free manual reset thermostatic switch comprising:

a base;

a thermostatic element mounted for flexing movement on said base andadapted to move from a first to a second position relative to said basein response to predetermined temperature conditions and to remain insaid second position independent of further changes in temperature;

a cover for said base and thermostatic element movable toward and awayfrom said base and held captive thereto;

a switch assembly including a first contact mounted within said coverand a contact arm one end of which is secured inside the cover andhaving a free end carrying a second contact normally engaged with saidfirst contact but movable out of engagement therewith;

an actuator adapted, when said thermostatic element moves into itssecond position, concurrently to move said contact arm to separate saidcontacts;

said cover adapted, when moved from a normal to a reset positionrelative to said base, to move said actuator to bias said element awayfrom its second and toward its first position whereby the contacts willremain separated and said thermostatic element will not move into itsfirst position while said element is subject to said predeterminedtemperature conditions and whereby the contacts will reclose and thethermostatic element will be moved into its first position in theabsence of said predetermined temperature conditions.

2. A thermostatic switch as set forth in claim 1 which further includesmeans biasing the cover and switch assembly away from the base into thenormal position thereof and in which the cover is moved against saidbias to said reset position whereby resetting of the thermostaticallytripped switch assembly is effected by pressing said cover toward thebase in the absence of said predetermined temperature conditions.

3. A thermostatic switch as set forth in claim 1 which further includesmeans biasing the cover and switch assembly toward said base and intothe normal position thereof and in which the cover is moved against saidbias to said reset position whereby resetting of the thermostaticallytripped assembly is effected by pulling said cover away from the base inthe absence of said predetermined temperature conditions.

4. A thermostatic switch as set forth in claim 2 wherein the actuator isa transfer pin slidably interposed between the thermostatic element andone side I of an intermediate portion of said contact arm and in whichthe cover includes a post adapted to engage the other sideof theintermediate portion of said movable arm.

5. A thermostatic switch as set forth in claim 3 in which the actuatoris a transfer pin coupling the thermostatic element and said movable armfor substantially conjoint movement, and said transfer pin includes anextension in sliding engagement with and having a lost-motion connectionwith said cover.

6. A thermostatic switch as set forth in claim 1 wherein the base isgenerally cup shaped and has an inwardly directed flange spaced from thebottom thereof and constituting means retaining said cover on the basefor limited movement relative thereto.

7. A thermostatic switch as set forth in claim 6 wherein the cover is ofgenerally inverted cup shape and has an outwardly directed flangereciprocally movable within said base.

8. A thermostatic switch as set forth in claim 7 which includes meansbiasing the cover away from the base.

' 9. A thermostatic switch as set forth in claim 7 which includes meansbiasing the cover toward the base.

10. A thermostatic switch as set forth in claim 7 which includes springmeans interposed between the cover and the base, said spring means beingconstituted by a spring washer.

11. A thermostatic switch as set forth in claim 7 which further includesan annular mamber interposed between the inner surface of the base andthe outer surface of the cover, said annular member having an inwardlydirected flange overlying the outwardly directed flange of said cover tolimit the movement of the cover relative to'the base.

12. A thermostatic switch as set forth in claim 7 in which thecup-shaped base is provided with a plurality of slots adapted totransitorily receive spacer shims to serve as spacer gages duringassembly of said cover and base thereby to establish the maximumdisplacement position of the cover relative to the base when forming theinwardly directed flange of the base.

13. A thermostatic switch as set forth in claim 4 wherein the post isintegrally formed with the cover.

14. A thermostatic switch as set forth in claim 4 wherein the post ismovable relative to the cover whereby the temperature at which thethermostatic element may be reset to its first from its second positionis adjustable.

1. A trip-free manual reset thermostatic switch comprising: a base; athermostatic element mounted for flexing movement on said base andadapted to move from a first to a second position relative to said basein response to predetermined temperature conditions and to remain insaid second position independent of further changes in temperature; acover for said base and thermostatic element movable toward and awayfrom said base and held captive thereto; a switch assembly including afirst contact mounted within said cover and a contact arm one end ofwhich is secured inside the cover and having a free end carrying asecond contact normally engaged with said first contact but movable outof engagement therewith; an actuator adapted, when said thermostaticelement moves into its second position, concurrently to move saidcontact arm to separate said contacts; said cover adapted, when movedfrom a normal to a reset position relative to said base, to move saidactuator to bias said element away from its second and toward its firstposition whereby the contacts will remain separated and saidthermostatic elEment will not move into its first position while saidelement is subject to said predetermined temperature conditions andwhereby the contacts will reclose and the thermostatic element will bemoved into its first position in the absence of said predeterminedtemperature conditions.
 2. A thermostatic switch as set forth in claim 1which further includes means biasing the cover and switch assembly awayfrom the base into the normal position thereof and in which the cover ismoved against said bias to said reset position whereby resetting of thethermostatically tripped switch assembly is effected by pressing saidcover toward the base in the absence of said predetermined temperatureconditions.
 3. A thermostatic switch as set forth in claim 1 whichfurther includes means biasing the cover and switch assembly toward saidbase and into the normal position thereof and in which the cover ismoved against said bias to said reset position whereby resetting of thethermostatically tripped assembly is effected by pulling said cover awayfrom the base in the absence of said predetermined temperatureconditions.
 4. A thermostatic switch as set forth in claim 2 wherein theactuator is a transfer pin slidably interposed between the thermostaticelement and one side of an intermediate portion of said contact arm andin which the cover includes a post adapted to engage the other side ofthe intermediate portion of said movable arm.
 5. A thermostatic switchas set forth in claim 3 in which the actuator is a transfer pin couplingthe thermostatic element and said movable arm for substantially conjointmovement, and said transfer pin includes an extension in slidingengagement with and having a lost-motion connection with said cover. 6.A thermostatic switch as set forth in claim 1 wherein the base isgenerally cup shaped and has an inwardly directed flange spaced from thebottom thereof and constituting means retaining said cover on the basefor limited movement relative thereto.
 7. A thermostatic switch as setforth in claim 6 wherein the cover is of generally inverted cup shapeand has an outwardly directed flange reciprocally movable within saidbase.
 8. A thermostatic switch as set forth in claim 7 which includesmeans biasing the cover away from the base.
 9. A thermostatic switch asset forth in claim 7 which includes means biasing the cover toward thebase.
 10. A thermostatic switch as set forth in claim 7 which includesspring means interposed between the cover and the base, said springmeans being constituted by a spring washer.
 11. A thermostatic switch asset forth in claim 7 which further includes an annular mamber interposedbetween the inner surface of the base and the outer surface of thecover, said annular member having an inwardly directed flange overlyingthe outwardly directed flange of said cover to limit the movement of thecover relative to the base.
 12. A thermostatic switch as set forth inclaim 7 in which the cup-shaped base is provided with a plurality ofslots adapted to transitorily receive spacer shims to serve as spacergages during assembly of said cover and base thereby to establish themaximum displacement position of the cover relative to the base whenforming the inwardly directed flange of the base.
 13. A thermostaticswitch as set forth in claim 4 wherein the post is integrally formedwith the cover.
 14. A thermostatic switch as set forth in claim 4wherein the post is movable relative to the cover whereby thetemperature at which the thermostatic element may be reset to its firstfrom its second position is adjustable.